Telemonitoring of biosignals is a growing area of research due to the aging world population. Telemonitoring can utilize a wireless body-area network (WBAN) consisting of wearable biosignal sensors equipped with ultra-low power radios. The measured data from each sensor on the patient can be sent to a central communication node (e.g., smartphone or personal computer), which can then send the data to a healthcare provider via the internet. Thus, the patient's health can be monitored continuously and remotely in real-time without the need for the patient to visit their doctor.
One of the major constraints in WBANs is power consumption, since these sensors (especially sensors internal to the body) can be meant to be used for weeks, months, and even years. If one looks to the WBAN to determine where, if anywhere, the power being consumed by the WBAN can be conserved, it can be seen that the power consumed by wirelessly transmitting the data to the central communication node is orders of magnitude higher than the power consumed by any other operation (e.g., analog-to-digital conversion and digital signal processing), and thus, must be minimized.
To enable real-time monitoring of the biosignals, it can also be desirable to have accurate timestamped data from the sensors in the WBAN. For example, if a sensor uses a low cost 32,768 Hz crystal oscillator with a frequency stability of 100 ppm, the time offset can be as high as 259 seconds after 1 month of use without any synchronization algorithm. Most of the synchronization algorithms presented in the literature require the exchange of dedicated timing messages containing digital timestamps on the network. However, this is not feasible for WBANs, due to the high power cost associated with transmitting messages.
In the prior art, a timestamp-free synchronization algorithm is proposed where no dedicated timing messages are exchanged; the synchronization algorithm is embedded in the existing network messages. Timing information can be communicated implicitly in the timing of the central communication node's response to the sensor node's message (as used in this specification, the term “implicit”, “implicit timing information” and similar terminology can be taken to mean timing information can be extracted from a more general information exchange between the sensor and central communication node, and the general information itself does not contain dedicated, explicit timing information). This concept works well for many networks, since synchronization can be achieved without the additional overhead and cost of exchanging dedicated timing messages. However, in WBANs, the sensors typically send their data to a central communication node, but do not necessarily need to receive a frequent number of packets from the central communication node. Thus, the prior art algorithm may not be appropriate for WBANs, since it does not account for any power constraints on the network nodes and requires a bidirectional message exchange.
In view of the above, it is an object of the present invention to provide a network and network time synchronization method that can be free from dedicated timestamp messages. Another object of the present invention is to provide network and network time synchronization method which can minimize power consumption. Still another object of the present invention can be to provide a network and network time synchronization method which minimizes unnecessary time stamped messages from the master node to the slave node(s). Another object of the present invention is to provide a network and network time synchronization method that can be relatively easy to implement in a cost-efficient manner.